[Elecraft] KPA500 delay in getting to full power

[Mike Schultz KS0T]

    A problem just showed up with my 4 month old amp. If I send a string of dashes at 30 Watts out of my K3, the KPA amp puts out around 120 Watts for the first second or two then goes up to the expected output of 480 Watts.  This is on 20 meters to a Dummy load through my KAT500 tuner in bypass.  The ACCY plug was disconnected and PTT was direct from K3 to KPA500.  Amp firmware was beta 1.33 but no change when I reverted to release V1.23.
Any ideas while I continue the CQWW SSB contest at a frustrating 100 Watts?

73, Mike KS0T